package jisuanke;

import java.util.Scanner;

public class 简单斐波那契 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        System.out.println(function(n));
    }

    public static int function(int n){
        if(n == 0){
            return 0;
        }
        if(n == 1){
            return 1;
        }
        return function(n-1) + function(n-2);
    }
}
